Question

lf A= {3, 6, 9, 12, 15, 18, 21} , B={4, 8, 12, 16, 20 }, C={2, 4, 6, 8, 10, 12, 14, 16} D={5, 10, 15, 20}; Find A - D

Answer 1

concept :- A - B shows the relative complement of the set, which represents members of set A which are not part of set B. see figure , here shaded region is shown, this shaded region indicates A - B.


here, A= {3, 6, 9, 12, 15, 18, 21},
B={4, 8, 12, 16, 20 },
C={2, 4, 6, 8, 10, 12, 14, 16},
D={5, 10, 15, 20}.

so, A - D = {3, 6, 9, 12, 15, 18, 21} - {5, 10, 15, 20}
here, you can see that 15 is present in both the sets. so, A - B will not contain 15 and will contain rest elements of A.
hence, A - D = {3, 6 9, 12, 18, 21}

Answer 2

Solution :

Given A = { 3,6,9,12,15,18,21 }

D = { 5,10,15,20 }

A-D = {x:x€A and x doesn't belongs to D}

= { 3,6,9,12,15,18,21 } - { 5,10,15,20 }

= { 3,6,9,12,18,21 }

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